1. Field of the Invention
This invention relates to data processing and more particularly the reading out at very high speed of data recorded on a film in the form of discrete levels of optical density located in a known format.
2. Description of the Prior Art
Prior art is described in U.S. Pat. No. 3,584,147, issued June 8, 1971, to Flory, in which successive frames are illuminated in time sequence by a strobe lamp of one color, while light of a different color is used for the synchronization signals, to eliminate crosstalk between the synchronization channel and the data channel.
A read-out system using spaced spots of light of different colors is described by Harris in IBM Technical Disclosure Bulletin, Volume 10, No. 12, May, 1968, page 1868, to sense the optical density at different points in the data frame. Harris assigns a separate color to each row of data and the rows are read by motion of a series of colored spots across the film. For each color channel there is provided one detector cell, part of an array of detector cells.
Corcoran, U.S. Pat. No. 3,739,154, issued June 12, 1973, contemplates the simultaneous scan of a plurality of recorded tracks in a recording medium during readout. Corcoran's invention resembles Harris' in that a separate detector cell is assigned to each row of data, and the rows are scanned simultaneously by motion of the light spot across the film.
Ketchledge, U.S. Pat. No. 3,099,820, issued July 30, 1963, reads data stored in the form of transparent colored squares on a film using a single detector array. A cathode ray tube is used to generate a sequence of colors for illuminating the film.
The patent to Weimer, U.S. Pat. No. 3,696,250, issued Oct. 3, 1972, describes a system for transferring the information from sensor elements into an output circuit where the elements are part of a two-dimensional array. Weimer does not suggest the desirability of combining his information transfer technique with an optical film reading system and does not hint at the advantages such a combination would possess if used for film reading.
Thus, although the prior art abounds with systems for reading data stored on film, it will be seen below that the present invention uses a novel approach and is capable of achieving higher speed.